1. Field of the Invention
The present invention relates to a steam condenser, and particularly, to a steam condenser having an improved layout of heat-transfer tubes constituting a group of tubes.
2. Description of Related Art
A steam condenser has a function to condense exhausted steam from a steam turbine and collect condensed water thereof. Steam condensers are widely used in steam turbine power plants. In general, a steam condenser has a container communicating with a steam exhaust port of the steam turbine, and the container includes a heat transfer tube group (hereinafter abbreviated as a tube group) consisting of a large number of arrayed heat transfer tubes through which a cooling medium flows.
Steam exhausted from the steam turbine flows down in the container of the steam condenser and contacts the tube group. Then, the steam is deprived of the latent heat by the cooling medium flowing through the heat transfer tubes. The steam is thereby condensed and collected as condensed water. In a conventional steam condenser, condensation of steam progresses due to the temperature difference between steam and the cooling medium. When being condensed, the temperature of steam is a saturation temperature corresponding to partial pressure of steam at the condensation surface.
However, the partial pressure of steam lowers roughly because of two factors. Accordingly, a reduction in temperature difference is thereby caused, so that the condensation performance (or heat exchange efficiency) deteriorates. One of the two factors is a pressure loss caused by flowage of steam. The other factor is increase in partial pressure of noncondensable gas due to concentration of noncondensable gas mixed in the steam. Therefore, it is important for a steam condenser to reduce loss of partial pressure of steam and to suppress concentration of noncondensable gas, in order to improve performance.
In general, the exhaust pressure of a steam turbine is related with the pressure loss of the steam condenser and the noncondensable gas density in the steam condenser. The exhaust pressure of the steam turbine is determined by adding the pressure loss of steam in the steam condenser to the pressure in the tube group where steam is condensed. Therefore, if the pressure loss of steam in the steam condenser is large, the exhaust pressure of the steam turbine is so high that the turbine output is lowered, deteriorating the power generation efficiency.
If there is a place where steam is stagnant, the concentration and the partial pressure of noncondensable gas increase. Then, the partial pressure of steam decreases. In such a case, total condensation rate is secured, so that back pressure of the turbine becomes higher.
Thus, reduction of the pressure loss of steam in the steam condenser and a smooth lead of steam to a gas cooling section without stagnation of steam in the tube group are significant technical subjects as indices of the performance of a steam condenser.
For these subjects, conventional steam condensers have been taking two major different measures. One of the measures is to provide a sufficiently large steam channel space in the periphery of the group of tubes arrayed in a relatively concentrated layout, for example, as disclosed in Japanese Patent Application Laid-Open Publication No. 8-226776.
The other measure is to provide a sufficient steam channel in the group of tubes arrayed sparsely as a whole over a broad range, for example, as disclosed in Japanese Patent Publication No. 55-36915.
In a conventional steam condenser, when replacing only the tube group with a new tube group, there is a case that the new group of tubes cannot be easily installed from either an opening part in an operation floor of a turbine building or an opening in a wall thereof. Therefore, it is necessary to construct the tube group in a block structure of blocks each having a size small enough to carry in. However, when constructing such a separable tube group, a problem arises in a biased steam flow into the tube group which is caused by turbine exhaust flow rate distribution.
In general, the farther from a main turbine shaft the turbine exhaust flowing into a container of a steam condenser is, the faster the flow rate is. The closer to the main turbine shaft the exhaust is, the slower the flow rate is. Therefore, of a steam flow introduced from an upper part of the steam condenser to a lower part thereof, the flow is fastest along a side wall of the container of the steam condenser.
Therefore, the tube group may be constructed to be separable, and plural inundation prevention plates for receiving condensed water may be provided in flow channels and the tube group, as a countermeasure against inundation (lowered heat transference caused by drops of condensed water). Besides, in this case, low-pressure parts may occur locally or steam may flow reversely to the outside from the inside of the tube group because of steam having a high flow rate in flow channels along the inundation prevention plates. Consequently, the performance of the steam condenser may deteriorate due to accumulation of gas or increase of pressure loss which is caused by occurrence of localized stagnancy.
A steam condenser condensing steam exhausted from a steam turbine according to an embodiment of the present invention comprises: a container having at least two side walls, configured to let the steam flow down therein from the steam turbine; plural heat transfer tubes arrayed below the steam turbine in the container, letting a cooling medium flow inside, contacting the steam flowing down to condense the steam, extending horizontally, and grouped into at least two upper heat transfer tube groups and at least two lower heat transfer tube groups, the two upper heat transfer tube groups being arranged horizontally with a gap therebetween, the two lower heat transfer tube groups being arranged horizontally with a gap therebetween below the two upper tube groups, and each of the heat transfer tube groups including the plural heat transfer tubes arrayed in a grid; plural tube plates supporting the plural heat transfer tubes; a baffle plate provided at a lower position between the lower heat transfer tube groups and extending in a horizontal direction, to obstruct a flow of steam; an inter-tube-group inundation prevention plate disposed at a position between the upper heat transfer tube groups and the lower heat transfer tube groups opposed vertically to each other, the plate extending in a horizontal direction to guide condensed water flowing down from upside, in a horizontal direction; an enclosure part disposed in each of the heat transfer tube groups, the enclosure part having top plate and two side plates, the top plate being disposed so as to extend substantially horizontally in parallel with the heat transfer tubes and having a gas extraction hole, the two side plates extending downward from the top plate and also extending in parallel with the heat transfer tubes with a space between each other, with the gas extraction hole and the plural heat transfer tubes interposed therebetween; and a gas extraction duct connected to the gas extraction hole to guide gas from the enclosure part to outside of the container.
A steam condenser condensing steam exhausted from a steam turbine according to another embodiment of the present invention comprises: A steam condenser condensing steam exhausted from a steam turbine, the steam condenser comprising: a container having at least two side walls, configured to let the steam flow down from the steam turbine; plural heat transfer tubes arrayed below the steam turbine in the container, letting a cooling medium flow inside, contacting the steam flowing down to condense the steam, extending horizontally, and grouped into at least two upper heat transfer tube groups and at least two lower heat transfer tube groups, the two upper heat transfer tube groups being arranged horizontally in the container with a gap therebetween, the two lower heat transfer tube groups being arranged horizontally with a gap therebetween below the two upper tube groups, and each of the heat transfer tube groups including the plural heat transfer tubes arrayed in a grid; plural tube plates supporting the plural heat transfer tubes; a baffle plate provided at a lower position between the lower heat transfer tube groups and extending in a horizontal direction, to obstruct a flow of steam; an inter-tube-group inundation prevention plate disposed at a position between the upper heat transfer tube groups and the lower heat transfer tube groups opposed vertically to each other, and extends in a horizontal direction to guide condensed water flowing down from upside, in a horizontal direction; a lower tube group enclosure part disposed in each of the lower heat transfer tube groups, the enclosure part having a first top plate and two side plates, the lower tube group first top plate being disposed so as to extend horizontally in parallel with the heat transfer tubes and having a gas extraction hole, and the two side plates extending downward from the first top plate and also extending in parallel with the heat transfer tubes with a space between each other, with the gas extraction hole and the plural heat transfer tubes interposed therebetween; an upper tube group enclosure part disposed in each of lower ends of the upper heat transfer tube groups at the sides close to the side walls of the container, the upper tube group enclosure part having an outer end plate standing from the inter-tube-group inundation prevention plates along an outer end of the upper heat transfer tube groups and having a gas extraction hole, and a second top plate connected to an upper end of the outer end plate and extending in parallel with the inter-tube-group inundation prevention plates, the plural heat transfer tubes being interposed between the upper tube group enclosure part and the inter-tube-group inundation prevention plates; and a gas extraction duct connected to the gas extraction holes of the first top plate of the lower tube group enclosure part and of the outer end plate of the upper tube group enclosure part, to guide gas from the lower tube group enclosure part and the upper tube group enclosure part to outside of the container.